Bladed impeller for turboblowers



Oct. 4, 1949'. K. BAUMANN 2,483,610

a BLADED IMPELLER FOR TURBOBLOWERS Filed Feb. 26, 1944 Patented on. 4, 1949 BEADED IMPELLEB FOR TURBOBLOWERS Karl Baumann, Mere, Knutsford, England, as-

signor, by mesne assignments, to the Minister of Supply in His Majesty's Government of the United Kingdom of Great Britain and Northern Ireland, London, England Application February 26, 1944, Serial No. 523,988 In Great Britain March 23, 1943 5 Claims.

This invention relates to the manufacture of bladed impellers for turbo-blowers or compressors and in particular to such impellers of the socalled double-entry, open-sided type, namely in which the impeller blades extend radially from a central hub and are so shaped as to allow of fluid entrance axially from either side of the impeller.

Such impellers are frequently required to be run at high speed imposing large centrifugal loads upon the blades, which members must also have adequate lateral rigidity.

Hitherto it has been customary to construct such impellers by machining from a solid disc to provide integral blades of the shape and rigidity required.

According to the present invention, in the manufacture of an impeller as above set forth, the blades are constructed separately from their supporting hub and each in two separate complementary portions, which may be, but are not necessarily, similar, adapted when assembled end-on to the circumferential surface or rim of the supporting hub and preferably united in sideby-side relationship with one another, namely with a side face, or edge, of one portion closely abutting a corresponding side face, or edge, of the complementary portion, to form in effect a unitary blade proper of substantial lateral stiffness and of the appropriate shape as to afford double-entry of workingiluid in the axial direction of the hub; for convenience of description, the separate complementary portions of a blade proper are hereinafter referred to as complementary halves" or half-blades.

In applying the invention, the actual shapes of the complementary halves of a blade proper, in the axial direction of the supporting hub and also in the radial direction, as well as their dimensions, and the angle of their general inclination each to the other when assembled as described will depend upon the conditions and circumstances in which the impeller is intended to be utilised. In some instances the surfaces of the complementary half-blades for a blade proper, which 'jointly provide the operating surface of the blade, either front or rear, may be fiat, whereas in other cases they may be of curved and regular or irregular formation according to cirand the adjacent blade proper; in the case of a star type impeller the complementary halves of a blade proper may be parallel sided, that is, as regards the faces jointly forming the operating surface, be it front or rear, of the blade proper, or alternatively they may be formed with a tapering section as between root and tip.

In practising the invention, it is preferred to attach the complementary halves of a blade proper to the supporting hub by arranging for their root ends to be retained in slots formed in the circumferential face or rim of the hub and extending generally in the axial direction thereof. Advanta-geously, either, or both of the slots for retaining the roots of the complementary halves of a blade proper may be inclined to the axis of the hub so that the two slots for complementary half-blades are inclined to one another and preferably constitute the flanks of a unitary or continuous V-shaped slot. Conveniently the joint between a root of a half-blade and the hub may be dovetailed, that is to say, the half-blade is formed at the root with a dovetailed section, the retaining slot therefor in the hub being correspondingly shaped.

Generally speaking, it is preferred to construct the complementary halves of a blade proper so that, when they are assembled on the supporting hub, each radius passing through the centre of Y gravity of a half-blade passes within the root section in the hub.

According to a preferred, and, incidentally, an important feature of the invention, the complementary halves of a blade proper are formed each with the end face at the root thereof inclined at an acute angle with respect to the free, or outer, edge vor face of the half-blade and therefore an obtuse angle with respect to the opposite, or inner, edge or face, namely that which is contiguous with, and preferably united to, the corresponding edge or face of the complementary half-blades; the peripheral face of the hub against which such root end will abut, or the axis of the slot for retaining said end root, is correspondingly inclined in the radial direction of the hub. In a preferred form the portions of the circumferential face or rim of the hub against which the root ends of the complementary halves of a blade proper abut, or the slots therein for retaining said root ends, are shaped to converge radially outwardly with respect to the axis of the hub. With this construction, the centrifugal force acting on the complementary halves of a blade proper during rotation of the impeller will tend to force them together and thus enhance the inherent strength of the construction. Thus, in

a preferred form, the two slots in the hub rim which accommodate two complementary halfblades are cut with their centre-lines co-planar in a plane not passing through the axis of the hub, the centre-lines being equally inclined to a line in that plane parallel to the hub axis.

In carrying out the invention it is contemplated to attach the two complementary halves.

of a blade proper together by weldingalong the contiguous edges or faces thereof, and for this purpose these faces may be suitably chamfered; likewise, the root ends of the complementary halves of a blade may be attached individually to the supporting hub also by welding.

The supporting hub may be in the form of a shaft or a disc attached to a shaft or two discs to which the complementary halves of a blade proper are individually attached and which in turn are attached to a common shaft.

Evidently, the invention may be applied either to the construction of an impeller having a single row of blades, or to one having several rows of blades.

In order that the invention may be fully understood and carried into effect, it will now be described, by way of example and with reference to the accompanying drawing, in its application to a bladed impeller for a turbo-blower or compressor, having a series of rows of double-entry open-sided blades arranged with the blading rows radiating outwardly from a central hub in accordance with the star type construction.

In the drawings, Fig. Let the left-hand side, shows in elevation and plan view two complementary half-blades constructed in accordance with the invention, while at the-.right-hand side of the figure is a perspective view of one of the halfblades;

Fig. 2 shows, at the left-hand side, in elevational view, part of a supporting hub to which the several pairs of half-blades for one blading row will be attached in accordance with the invention, while at the right-hand side is a perspective view of part of the hub;

Fig. 3 shows, at the left-hand side, in sectional views, part of an assembled impeller according to the invention, one section (the upper) being taken in the planes of the two complementary half-blades and the other (lower) taken in a plane parallel with the axis of the impeller and cutting the complementary half-blades intermediately, while at the right-hand side is a perspective view of part of the assembled impeller as it concerns one half-blade.

In the embodiment of the invention illustrated, and now to be described, the blades for each blade row of the impeller are constructed each in two similar halves, designated a and b, each such half-blade being in the form of a thin elongated member having parallel side faces al, a2, or bl, b2; the half-blades are also formed with a tapering cross-section as between the root end and the tip end (Fig. 1, right-hand side). For half-blade a, the end face a3 at the root is cut to an acute angle with respect to the edge at which will be the entering or free edge for the blade proper, and likewise for half-blade b, the root end face b3 is cut to the same acute angle with respect to the edge bl which will be the entering or free edge for the blade proper; the sides a2, b2 are preferably chamfered as between the tips and nearly the roots of the blades, for a purpose hereinafter indicated. Further, the half-blades a, b are formed at the root each with 10 in one piece or it may be formed in two separate pieces and assembled end to end on the shaft.

Whichever be the precise mode of construction followed, the disc AB for each blade row is formed with parallel end faces while its periphery or rim is constituted by two frusto-conical surfaces A0, B0, equally inclined to the axis, represented by the chain-dotted line, so as to converge radially outwardly therefrom.

Along the inclined peripheral surface A is a series of circularly distributed and equi-spaced grooves Al and likewise along the surface 130 is a similar series of circularly distributed and equispaced grooves Bl. The grooves Al are inclined acutely to the axis and the grooves Bl are similarly inclined acutely to the axis but oppositely to the inclination of the grooves AI; thus, in effect, the grooves for each pair Al, BI form a continuous elongated V-shaped slot extending from one end face of the disc AB to the opposite end face, and with the apices of the several v-shaped slots Al, Bi lying in a central plane of the disc which is at right angles to the axis.

Each slot Al is formed with the outermost edges A2, A3 respectively, that is at the frusto-conical surface A0, parallel with one another while the floor A4 of the slot is parallel with said surface A0; moreover, each slot is formed with a dovetailed cross-section corresponding to the dovetail cross-section A4 for a half-blade. The slots Bl are similarly shaped.

The several pairs of complementary halfblades a, b for each row of blades proper are assembled on the supporting hub with the root (:4 of one half-blade inserted in theinclined groove Al forming one flank of the V-shaped slot for the blade and with the root bl of the complementar y half-blade inserted in the inclined groove Bl forming the other flank of said V-shaped slot, the complementary half-blades being brought together so that the radial face A2 of one halfblade is in abutting relation with the corresponding radial face B2 of the complementary halfblade in a central plane of the disc AB which is at right angles to the axis.

When assembled the complementary halfblades a, b for a blade proper are attached together by welding along their contiguous and preferably chamfered faces a2, b2 so as effectively to form a rigid unitary blade. The half- 60 blades may be further rigidly attached to the disc AB by welding between the roots at, bl

and the edges of their retaining V-shaped slot AIBI.

Although in the particular embodiment 65 illustrated the complementary half-blades are similar and similarly inclined to the hub, thus giving a symmetrical construction throughout, it will be appreciated that such symmetrical construction is by no means the one which need be followed; in fact, as will be evident, the

method of construction according to this invention is especially advantageous in that it permits of variation in the mutual inclination of the retaining slots in the hub and the choice of 75 the individual blade dimensions and shape to suit any particular requirements as to the shape and inclination of the operating surfaces of the blades of the impeller.

In the drawing, it will be observed that the grooves Al, Bl forming the V-shaped retaining slot for a blade are formed each with a nick adjacent the central plane of the supporting disc AB. By way of explanation, it is pointed out that the grooves Al, Bl may be formed conveniently by use of a suitable slot-cutting machine. With such machine, the shaping tools for cutting the slots would normally move in the directions indicated by the respective arrows in Fig. 3, and the shaping tool which cuts down one side A2 of the groove Al in the inclined face A0, cuts a nick B5 in the other inclined face 130 when emerging, while the shaping tool which cuts the opposing face A3 of the same groove emerges clear at the commencement of the side B3 of the groove Bl in the face B that is, without mutilating the face B0; likewise, the shaping'tool which cuts down the side B2 of groove Bl cuts a nick A in the face A0 when emerging, while the tool which cuts down the side B3 emerges clear at the face All, that is, without mutilating said face All. In other words, the nicks A5, B5 have no particular function in the assembled impeller but arise merely in the machining of the retaining slots for the blades.

In conclusion, it is pointed out that an im portant feature of the construction according to the invention resides in the arrangement of retaining slots for the roots of respective complementary half-blades so that centrifugal force acting on the complementary'half-blades during rotation of the impeller will tend to force said half-blades together thus to enhance the inherent strength of the structure. In this connection, it may be mentioned that tests have shown that for the appropriate root dimensions, the complete blades built up in accordance with the invention will withstand in safety such heavy centrifugal and bending stresses as are known to be likely to be encountered in respect of bladed impellers of the character in question for turbo-blowers or compressors operated at high speeds.

What I claim as new and desire to secured by Letters Patent of the United States is:

1. A double-entry open-sided bladed blower comprising a rotary shaft, a hub thereon formed on its circumferential surface with two grooves extending from the end faces of the hub to a location of intersection with one another which is at a greater distance radially from the axis of the shaft than are the opposite ends of said grooves, and complementary half-blades insertable one in each slot and adapted at least partially to abut one another in a plane passing through the intersection of the grooves.

2. A double-entry open-sided bladed blower comprising a rotary shaft, a hub thereon formed on its circumferential surface with two rectilinear grooves intersecting at one end in alocation further removed radially outwardly from the rotary axis of the shaft than are their opposite and axially outer ends, and two complementary half-blades rooted one in each groove, at least one-half blade being insertable from the axially outer end of the appertaining groove in- 3. A bladed blower of the double-entry open- I sided type comprising a rotary shaft, a hub thereon having oppositely inclined frusto-conical surfaces tapering radially outwardly from the axial end faces of said hub, said frustoconical surfaces being formed each with a plurality of grooves circularly distributed around the rotary axis and each groove for one said surface extending from an axial end-face of the hub into intersecting relation with a groove of the other said surface, and complementary halfblades retainably insertable one in each of two intersecting grooves and adapted at least partially to abut one another along the plane of intersection of the grooves.

4. A double-entry open-sided bladed blower comprising a shaft, a hub thereon formed on its peripheral surface with a plurality of V-shaped rectilinear grooves circularly distributed around the longitudinal axis of the shaft, each with its apex further removed radially outwardly from the axis of the shaft than are its outer ends and each having the centre lines of its rectilinear inclined portions located in a plane which does not intersect said axis, together with a plurality of blades each formed in two complementary portions retainably inserted in respective rectilinear inclined portions of a groove with one blade portion abutting the other along an edge at right'angles to the longitudinal axis of the shaft.

5. A bladed blower of the double-entry open-sided type comprising a rotary shaft, a hub thereon having a peripheral surface formed in two portions which converge radially outwardly with respect to the rotary axis of the shaft and are formed with respective rectilinear grooves of dovetailed cross-section extendin from the end-faces of the hub to a location of intersection with one another which is further removed radially outwardly from the axis of said shaft than are the opposite ends of said grooves, and which grooves are oppositely inclined with respect to the direction of rotation of the shaft, together with complementary halfblades rooted one in each groove so as to abut one with the other half-blade along an edge at right angles to the axis of the shaft, said halfblades being formed each at the root with dovetailed cross-section conforming to that of its its groove, and said half-blades being individually secured to the hub by welding along the edges of the groove and secured one to the other by welding along their abutting edges.

KARL BAUMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 710,884 Parsons Oct. 7, 1902 1,535,417 Huff Apr. 28, 1925 1,793,468 Densmore Feb. 24, 1931 1,829,179 Back Oct. 2'7, 1931 1,891,612 Schmidt Dec. 20, 1932 1,917,037 Jessop et al. July 4, 1933 

